Damaged dam threatens Northern California towns

his Friday, Feb. 10, 2017 image from video provided by the office of Assemblyman Brian Dahle shows water flowing over an emergency spillway of the Oroville Dam in Oroville, Calif., during a helicopter tour by the Butte County Sheriff's office. About 150 miles northeast of San Francisco, Lake Oroville is one of California’s largest man-made lakes, and the 770-foot-tall Oroville Dam is the nation's tallest. (Josh F.W. Cook/Office of Assemblyman Brian Dahle via AP)

Nearly 200,000 people, who evacuated Sunday over fears that a damaged spillway at Lake Oroville could fail and unleash a wall of water, have to stay away indefinitely while officials race to repair it before more rains arrive Thursday, according to the Associated Press.

A flash flood warning is in effect Tuesday after the spillway — which lets excess water out when the level gets too high — suffered massive damage over the weekend, according to CNN.

If the spillway fails, it could flood communities downstream with what one official warned could be a "30-foot wall of water."

Nation's tallest dam

The Gold Rush town of Oroville, in the Sierra Nevada foothills some 70 miles northeast of Sacramento, is nestled near the foot of the dam, which was completed in 1968 and at 770 feet is the nation's tallest.

Over the weekend, the swollen lake spilled down the unpaved, emergency spillway for nearly 40 hours, leaving it badly eroded and with a huge hole caused by a chunk of concrete.

On Monday, helicopters and trucks were trying to fill in the damaged area with giant bags full of rocks. The water level was slowly dropping and the amounts being discharged at the main spillway are the same as are normally released this time of year.

Rainfall over the next week could total 5 to 12 inches and will likely push hundreds of billions of water back into Lake Oroville, according to CNN Senior Meteorologist Dave Hennen.

Mass evacuations

Officials are defending the decision to suddenly call for mass evacuations late Sunday afternoon, just a few hours after saying the situation was stable, forcing families to rush to pack up and get out.

"There was a lot of traffic. It was chaos," said Robert Brabant, an Oroville resident who evacuated with his wife, son, dogs and cats. "It was a lot of accidents. It was like people weren't paying attention to other people," reported the Associated Press.

Continue for more photos...

This Feb. 11, 2017, photo released by the California Department of Water Resources shows the main spillway, bottom, and an auxiliary spillway, upper, of the Oroville Dam at Lake Oroville in Oroville, Calif. Water will continue to flow over the emergency spillway at the nation's tallest dam for another day or so, officials said Sunday. (Albert Madrid/California Department of Water Resources via AP)

This Saturday, Feb. 11, 2017, aerial photo released by the California Department of Water Resources shows the damaged spillway with eroded hillside in Oroville, Calif. Water will continue to flow over an emergency spillway at the nation's tallest dam for another day or so, officials said Sunday. (William Croyle/California Department of Water Resources via AP)

Water rushes down the Oroville Dam spillway, Thursday, Feb. 9, 2017, in Oroville, Calif. State engineers on Thursday discovered new damage to the Oroville Dam spillway, the tallest in the United States, though they said there is no harm to the nearby dam and no danger to the public. Earlier this week, chunks of concrete went flying off the spillway, creating a 200-foot-long, 30-foot deep hole. (AP Photo/Rich Pedroncelli)

Construction equipment moves piles of rock at a staging area near the Oroville Dam, Monday, Feb. 13, 2017, in Oroville, Calif. State officials have discussed using helicopters to drop loads of rock on the damaged emergency spillway of the dam. (AP Photo/Rich Pedroncelli)

The water from the Feather River flows through Oroville, Calif., Monday, Feb. 13, 2017. Authorities warned the emergency spillway of the Oroville Dam could fail at any time unleashing uncontrolled flood waters on towns below. (AP Photo/Rich Pedroncelli)

Evacuees from city's surrounding the Oroville Dam line up for dinner at a shelter Monday, Feb. 13, 2017, in Chico, Calif. The thousands of people who were ordered to leave their homes after a damaged California spillway threatened to unleash a 30-foot wall of water may not be able to return until significant erosion is repaired, authorities said Monday. (AP Photo/Marcio Jose Sanchez)

Kendra Curieo waits in traffic to evacuate Marysville, Calif., Sunday, Feb. 12, 2017. Thousands of residents of Marysville and other Northern California communities were told to leave their homes Sunday evening as an emergency spillway of the Oroville Dam could fail at any time unleashing flood waters from Lake Oroville, according to officials from the California Department of Water Resources. (AP Photo/Rich Pedroncelli)

A helicopter lowers a bag of rocks to be dropped on a hole on the lip of the Oroville Dam's emergency spillway Monday, Feb. 13, 2017, in Oroville, Calif. The barrier, at the nation's tallest dam, is being repaired a day after authorities ordered mass evacuations for everyone living below the lake out of concerns the spillway could fail. (AP Photo/Rich Pedroncelli)

Water gushes from the Oroville Dam's main spillway Tuesday, Feb. 14, 2017, in Oroville, Calif. Crews working around the clock atop the crippled Oroville Dam have made progress repairing the damaged spillway, state officials said Tuesday. (AP Photo/Marcio Jose Sanchez)

A gazebo is submerged from the overflowing Feather River downstream from a damaged dam at Riverbend Park Tuesday, Feb. 14, 2017, in Oroville, Calif. (AP Photo/Marcio Jose Sanchez)

A building is submerged from the overflowing Feather River downstream from a damaged dam at Riverbend Park on Tuesday, Feb. 14, 2017, in Oroville, Calif. (AP Photo/Marcio Jose Sanchez)